Sorry for the double post, but....
If you REALLY want to use avi, what has probably happened to produce the echoing effect, is that mayhaps, whatever you are using to convert has integrated both audio tracks to play at the same time. You may want to play with whatever you are using for conversion.
In either case, we would reccomend that you watch it in MKV if at all possible
If you are having issues with MKV, Head to the Leeching & Technical Problems Forum